Electrical bar latching for low stiffness flexure mems actuator

ABSTRACT

A MEMS actuator including buckled flexures and a method of assembling the actuator are described. The assembled MEMS actuator includes an inner frame; an outer frame including latched electrical bars, where a first of the latched bars includes a latch protrusion secured to a corresponding latch groove of a second of the latched bars; and buckled flexures coupling the inner frame to the outer frame. The flexures are buckled during assembly of the MEMS actuator by incorporating the electrical bar latching mechanism into the design of the outer frame of the MEMS actuator. In one implementation, the MEMS actuator is assembled by providing a MEMS actuator with unbuckled flexures coupling the outer frame of the MEMS actuator to an inner frame of the MEMS actuator, where the outer frame includes unlatched electrical bars, and latching the electrical bars of the outer frame, resulting in buckled flexures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/447,940, filed on Mar. 2, 2017, which is adivisional application of U.S. patent application Ser. No. 14/819,413,filed on Aug. 5, 2015, which is a continuation-in-part of U.S. patentapplication Ser. No. 14/677,730 filed Apr. 2, 2015, which claims thebenefit of U.S. Provisional Patent Application No. 61/989,457 filed May6, 2014, each of which is incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates generally to low stiffness flexures, andmore particularly, to an electrical bar latching structure and methodthat may be used to buckle the flexures during assembly of actuators andmotion stages such as, for example, motion stages formicroelectromechanical systems (MEMS).

BACKGROUND

Flexures are used in systems where there is motion between one portionof the system and another. In order to create the motion, there must bea force. In some cases, this force comes from an actuator or motor thatprovides a controlled force that creates movement. In such systems,flexures are usually used to connect the moving portion of the system tothe stationary portion of the system. The flexure must be designed sothat its stiffness is low enough so as to not impede motion in thedesired direction. In particular, to reduce the force requirements onthe actuator or motor, the stiffness of the flexure must be as low aspossible in the movement direction.

During design of a low stiffness flexure, the cross section of theflexure is usually designed to be as small as possible along thedirection of bending, and the length is made as long as possible.However, there are limits on the design of the dimensions ofconventional flexures. In some systems, these dimensions are limited byfabrication limits. For example, stamped metal flexures cannot be madetoo thin or too long without affecting handling and manufacturability.In other systems, the desire to make the cross section of the flexure assmall as possible conflicts with other system requirements. For example,if the flexure is designed to carry electricity, making the flexurecross section very small increases the resistance, which wastes powerand can lead to failure if enough current flows through the flexure.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with embodiments of the technology disclosed herein, AMEMS actuator including buckled flexures and a method of assembling theactuator are described. In one embodiment, the MEMS actuator includes aninner frame; an outer frame including a plurality of latched electricalbars, where a first of the plurality of latched bars includes a latchprotrusion secured to a corresponding latch groove of a second of theplurality of latched bars; and a plurality of buckled flexures couplingthe inner frame to the outer frame. In embodiments, the plurality ofbuckled flexures electrically and mechanically couple the inner frame tothe outer frame.

In one embodiment, the plurality of latched electrical bars consists ofthe first and the second latched bars. In this embodiment, each of thefirst and second latched bars is coupled to the inner frame by acorresponding plurality of buckled flexures, and the first latched barincludes a plurality of latch protrusions secured to a correspondingplurality of latch grooves of the second latched bar. In an alternativeembodiment, the plurality of latched electrical bars include fourlatched electrical bars, and each of the four electrical bars is coupledto the inner frame by a corresponding plurality of buckled flexures.

In one embodiment, a MEMS actuator may be assembled by providing a MEMSactuator with unbuckled flexures coupling an outer frame of the MEMSactuator to an inner frame of the MEMS actuator, where the outer frameincludes a plurality of unlatched electrical bars; and latching theplurality of electrical bars by securing a latch protrusion of a firstof the plurality of electrical bars to a corresponding latch groove of asecond of the plurality of electrical bars, where the flexures are in abuckled state when the electrical bars are latched. In implementationsof this embodiment, latching the plurality of electrical bars includescompressing the unbuckled flexures of the MEMS actuator along an axialdirection from the outer frame to the inner frame.

As illustrated by these embodiments, the MEMS actuator flexures may bebuckled during assembly of the MEMS actuator by incorporating anelectrical bar latching mechanism into the design of an outer frame ofthe MEMS actuator. Accordingly, the process of buckling the flexures maybe seamlessly integrated into a MEMS actuator assembly process.

Other features and aspects of the disclosure will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresin accordance with various embodiments. The summary is not intended tolimit the scope of the invention, which is defined solely by the claimsattached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technology, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments of the disclosedtechnology. These drawings are provided to facilitate the reader'sunderstanding of the disclosed technology and shall not be consideredlimiting of the breadth, scope, or applicability thereof. It should benoted that for clarity and ease of illustration these drawings are notnecessarily made to scale.

FIG. 1 is a plan view of an example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 2A is an edge view of the flexure of FIG. 1 as fabricated.

FIG. 2B is an edge view of the flexure of FIG. 1 in a buckled state.

FIG. 3 is a Force versus Displacement plot of an example embodiment of aflexure in accordance with the disclosed technology.

FIG. 4A is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 4B is a three-dimensional perspective view of the flexure of FIG.4A as fabricated.

FIG. 4C is a three-dimensional perspective view of the flexure of FIG.4A in a buckled state.

FIG. 5 is a Force versus Displacement plot of the flexure of FIG. 4A.

FIG. 6 is a Biased Force versus Biased Axial Displacement plot of theflexure of FIG. 4A in a buckled state.

FIG. 7 is a Tangential Force versus Tangential Displacement plot of theflexure of FIG. 4A in a buckled state.

FIG. 8 is a plan view of an example embodiment of a stage using an arrayof flexures in accordance with the disclosed technology.

FIG. 9 is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 10 is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 11 is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 12 is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 13 is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 14 is a plan view of another example embodiment of a flexure inaccordance with the disclosed technology.

FIG. 15 is a plan view of an example embodiment of a variable widthflexure in accordance with the disclosed technology.

FIG. 16 is a Normalized Force versus Normalized Displacement plotshowing the performance of different flexure designs in accordance withvarious embodiments of the disclosed technology.

FIG. 17A is a top plan view of an example embodiment of an offset layerflexure as fabricated in accordance with the disclosed technology.

FIG. 17B is a bottom plan view of the offset layer flexure of FIG. 17Aas fabricated.

FIG. 17C is a three-dimensional perspective of the offset layer flexureof FIG. 17A in a buckled state.

FIG. 18A is a plan view of an example embodiment of a split root flexureas fabricated in accordance with the disclosed technology.

FIG. 18B is a plan view of the split root flexure of FIG. 18A asfabricated

FIG. 18C is a three-dimensional perspective of the split root flexure ofFIG. 18A in a buckled state.

FIG. 19A is a plan view of an example embodiment of a flexure comprisingdifferent length layers in accordance with the disclosed technology.

FIG. 19B is a three-dimensional perspective view of the flexure of FIG.19A.

FIG. 20A illustrates a plan view of an actuator that may use thedisclosed flexures in accordance with embodiments of the disclosedtechnology.

FIG. 20B illustrates a cross-sectional view of an actuator that may usethe disclosed flexures in accordance with embodiments of the disclosedtechnology.

FIG. 20C illustrates a plan view of an actuator that may use thedisclosed flexures in accordance with embodiments of the disclosedtechnology.

FIG. 20D illustrates a cross-sectional view of an actuator that may usethe disclosed flexures in accordance with embodiments of the disclosedtechnology.

FIG. 21 is an operational flow diagram illustrating a method ofassembling a MEMS actuator for an image sensor package by latchingelectrical bars of an outer frame of the actuator in accordance with thedisclosed technology.

FIG. 22A illustrates an example MEMS actuator with an outer frameincluding four electrical bars that have not been latched in accordancewith the disclosed technology.

FIG. 22B is a magnified view of the latching mechanisms of the MEMSactuator of FIG. 22A.

FIG. 22C illustrates the MEMS actuator of FIG. 22A after the electricalbars have been latched.

FIG. 22D is a magnified view of the latching mechanisms of the MEMSactuator of FIG. 22C.

FIG. 23A illustrates another example MEMS actuator with an outer frameincluding four electrical bars that have not been latched in accordancewith the disclosed technology.

FIG. 23B is a magnified view of the latching mechanisms of the MEMSactuator of FIG. 23A.

FIG. 23C illustrates the MEMS actuator of FIG. 23A after the electricalbars have been latched.

FIG. 23D is a magnified view of the latching mechanisms of the MEMSactuator of FIG. 23C.

FIG. 24A illustrates an example MEMS actuator including an inner frameand an outer frame with two electrical bars that have not been latchedin accordance with the disclosed technology.

FIG. 24B illustrates the MEMS actuator of FIG. 24A after the electricalbars have been latched.

FIG. 25 illustrates an exploded perspective view of an exampleembodiment of placement of a MEMS actuator in a rigid circuit board inaccordance with the technology disclosed herein.

FIG. 26 is an exploded perspective view of an example image sensorpackage utilized in accordance with various embodiments of thetechnology disclosed herein.

The figures are not intended to be exhaustive or to limit the inventionto the precise form disclosed. It should be understood that theinvention can be practiced with modification and alteration, and thatthe disclosed technology be limited only by the claims and theequivalents thereof.

DETAILED DESCRIPTION

In accordance with various embodiments of the disclosed technology, newflexures are disclosed that include a first end connected to a firstframe, a second end connected to a second frame, and a buckled sectionconnecting the first end to the second end. The disclosed flexuresoperate in the buckling state without failure, thereby allowing thestiffness of the flexure to be several orders of magnitude softer thanwhen operated in a normal state. The flexures may be used in actuatorsand motion stages such as, for example, motion stages formicroelectromechanical systems (MEMS). In one particular embodiment, theflexures may be implemented in a MEMS actuator that moves an imagesensor of a camera package.

In various embodiments, illustrated below, the buckled section (i.e.,flexible portion) of the flexures is designed to be flexible such that across section of the flexible portion along its direction of bending(i.e., thickness and width) is small, while its length is relativelylong. For example, in embodiments the flexible section may be 10 to 30micrometers wide, 1 to 3 micrometers thick, and 500 to 800 micrometerslong. In one particular embodiment, the flexible section is 25micrometers wide, 1.5 micrometers thick, and 600 micrometers long.Additionally, the flexures may be designed to fit geometric constraintsand minimize stiffness and stress of the deformed flexure.

In embodiments, the flexures may be manufactured using MEMS technologyby patterning their design using photolithography and etching apolysilicon layer deposited on a silicon wafer coated with oxide. Inadditional embodiments, the flexures may be fabricated using a varietyof processes such as, for example, stamping, etching, laser cutting,machining, three dimensional printing, water jet cutting, etc. A varietyof materials may be used to form the flexures, such as, for example,metal, plastic, and polysilicon. In implementations, the flexures maycomprise one layer, two layers, or three layers of these materials. Inone embodiment, a flexure is formed of layers of polysilicon and metal,whereby the polysilicon layer provides improved flexibility andreliability and the metal layer provides improved electricalconductivity. In further embodiments, further described below, theflexure may have a variable width, split layers, offset layers, or somecombination thereof to achieve desired properties such as electricalconductivity and flexibility. As would be appreciated by one havingskill in the art, other combinations of materials may be used to achievethe desired properties of the flexures.

In additional embodiments, described below, the flexures may be buckledduring assembly of a MEMS actuator by incorporating an electrical barlatching mechanism into the design of an outer frame of the MEMSactuator. Accordingly, the process of buckling the flexures may beseamlessly integrated into a MEMS actuator assembly process.

FIG. 1 is a plan view of an exemplary flexure 100 in accordance with oneembodiment. As illustrated, flexure 100 comprises a first support end111, a second support end 112, and a flexible portion 113 connectingsupport end 111 to support end 112. As described above, in variousembodiments flexible portion 113 is designed to be flexible such that across section of portion 113 along its direction of bending (i.e.,thickness and width) is small, while its length is relatively long.FIGS. 2A-2B illustrate edge views of flexure 100. FIG. 2A illustratesflexure 100 in a pre-buckled state after fabrication. FIG. 2Billustrates flexure 100 in a buckled state. In one embodiment,illustrated by FIG. 2B, flexure 100 transitions to the buckled stateafter support end 112 is displaced toward support end 111, therebycausing flexible portion 113 to buckle up or down. Because the thicknessof example flexure 100 is smaller than its width, flexure 100 buckles upor down as shown in FIG. 2B. In other embodiments where the thickness ofthe flexure is greater than its width, the flexible portion may bucklesideways.

FIG. 3 is a Force versus Displacement plot of an example embodiment of aflexure in accordance with the disclosed technology. As illustrated,there is a pre-buckle regime or state in which the stiffness of theflexure, calculated as the change in displacement divided by the changein force, is relatively high. Once the flexure buckles, the flexureenters a post-buckle regime in which the stiffness of the flexure isdramatically reduced. By operating in the post-buckle regime, thestiffness of the flexure is dramatically lowered. Accordingly, invarious embodiments of the disclosed technology, the flexure operates inthe post-buckle regime (e.g., as illustrated by FIG. 2B) as opposed tothe pre-buckle or fabricated regime (e.g., as illustrated by FIG. 2A).To prevent failure of the flexure, in various embodiments a motionlimiter that limits motion of the flexure may be included in a system(e.g., actuator) that includes the flexure.

FIG. 4A is a plan view of another example flexure 200 in accordance withthe disclosed technology. As illustrated, flexure 200 comprises a firstsupport end 211, a second support end 212, and a flexible portion 213connecting first support end 211 and second support end 212. Likeflexure 100, flexure 200 buckles in radial directions between supportends 211 and 212 and has low stiffness in the post-buckle regime.Additionally, the design of flexure 200 provides low stiffness in atangential direction to support ends 211 and 212. In particular, flexure200 has a “V”-shaped design comprising two long and straight portions242, curved portions 241 connecting straight portions 242 to supportends 211-212, and a curved portion 243 connecting straight portions 242together.

In various embodiments, the curvatures of curved portions 241-242, theangle of the “V” and the length of straight portions 242 are designed tofit geometric constraints and minimize stiffness and stress of thedeformed flexure. For example, in one particular embodiment the angle ofthe “V” shape can be 35 degrees, the radii of curvatures 241 and 243 canbe 50 micrometers, the length of the straight portions 242 can be 650micrometers, and the separation between the support ends 211 and 212 canbe 700 micrometers.

FIGS. 4B-4C illustrate three-dimensional perspective views of flexure200. FIG. 4B illustrates flexure 200 as fabricated. FIG. 4C illustratesflexure 200 in a buckled state. In one embodiment, illustrated by FIG.4C, flexure 200 transitions to the buckled state after support end 212is deflected toward support end 211, thereby causing flexible portion213 to buckle in three dimensions. Because the thickness of exampleflexure 200 is smaller than its width, and because of the “V”-shapedgeometric design, flexure 200 buckles in three dimensions. This ensuresthat the buckled flexure has very low stiffness between support ends 211and 212 in both radial and tangential directions (i.e., x and ydirections shown in FIGS. 4B-4C).

FIG. 5 is a biased Force versus biased Displacement plot of flexure 200that was calculated using finite element analysis. As illustrated, thereis a pre-buckle regime with low axial displacement of moving support end212, in which the stiffness of flexure 200, calculated as the change indisplacement divided by the change in force, is relatively high. Thispre-buckle regime between zero axial displacement and approximately 0.05mm axial displacement corresponds to the shape shown in FIG. 4B. Afterflexure 200 buckles, the stiffness of the flexure is dramaticallyreduced. This post-buckle regime beyond approximately 0.15 mm axialdisplacement corresponds to the shape shown in FIG. 4C. In thisembodiment, there is a gradual transition regime between the pre-buckleand post-buckle regimes between approximately 0.05 mm and 0.15 mm axialdisplacement. By operating in the post-buckle regime, the stiffness ofthe flexure is dramatically lowered. As illustrated by FIG. 5, in thepost-buckle regime the stiffness of the flexure may be several orders ofmagnitude less than in the pre-buckle regime. Accordingly, in variousembodiments of the disclosed technology, the flexure operates in thepost-buckle regime (e.g., as illustrated by FIG. 3C) as opposed to thepre-buckle or fabricated regime (e.g., as illustrated by FIG. 3B).

FIG. 6 is a Biased Force versus Biased Displacement plot of flexure 200in a buckled state. As illustrated, flexure 200 is pre-deformed axiallyby displacing the moving support end 212 toward the stationary supportend 211 by 300 micrometers. The change in force corresponding to axialdisplacement toward the biased position is shown. The force required togenerate a displacement of 150 micrometers to the biased position isless than 0.9 micro-Newtons. In embodiments, the biased force versusbiased displacement may be nonlinear and asymmetric. However, since theflexure is softer than the system's stiffness in various embodiments,the nonlinearity that flexure 200 may introduce to the system isnegligible.

As described above, flexure 200 is pre-deformed axially to the biasedposition by displacing moving support end 213 toward stationary supportend 212 (e.g., by 300 micrometers). Afterward, the tangential forcecorresponding to tangential displacement may be measured and plotted asshown in FIG. 7. As illustrated, the force required to generate atangential displacement of 150 micrometers is less than 2.5micro-Newtons. The force is linear within the range of ±0.12micrometers, and starts to curve outside of this range. However, sincethe flexure is very soft in various embodiments, the nonlinearity thatflexure 200 may introduce to the system is negligible. In variousembodiments, the plots of FIGS. 6 and 7 may be used to design a fullflexure system.

FIG. 8 is a plan view of an example embodiment of a stage using an arrayof flexures in accordance with the disclosed technology. As illustrated,the stage includes a movable platform 311 connected to rigid bars orsupport ends 312 by flexure arrays 313. In this embodiment, for each ofthe flexures of flexure arrays 313 the first support end is part ofmovable platform 311 of the stage, the second support end is directlyconnected to one of rigid bars 312, and a flexible portion connects thefirst support end (movable platform 311) to the second support end(rigid bars 312). In various embodiments, Illustrated by FIG. 8, lowstiffness in two-dimensional motion may be achieved by pushing the rigidbars 312 toward each other (e.g., in the illustrated y direction) suchthat the flexures of flexure arrays 313 enter the post-buckle regime intheir full motion range. In these embodiments, the forces exerted by theflexure arrays 313 may balance out on both sides such that there is nonet force on platform 311.

In various embodiments, the stage and/or a system including the stagemay include motion limiters that limit horizontal and vertical motion ofmovable platform 311, and correspondingly, the flexures. For example, inFIG. 8 the system includes motion limiters 381 that limit motion in thevertical y direction, as well as motion limiters 382, that limit motionin the horizontal x direction. As illustrated, motion limiters 381 areincorporated into rigid bars 312, thereby preventing excessive movementof the first support ends of flexures 313 with respect to the secondsupport ends. Motion limiters 382 prevent horizontal over displacementof the movable platform 311 relative to rigid bars or support ends 312.Accordingly, motion limiters 381-382 may prevent failure of the buckledportion of flexures 313 due to excessive displacement in the x-y plane.

In additional embodiments, the flexures 313 may carry electrical currentfrom the movable platform 311 to the rigid ends 312. In theseembodiments, the flexures 313 may carry electrical current to anelectrical component of the stage (e.g., an image sensor). For example,electrical pads may contact an electrical component of movable platform311 and a circuit board of rigid ends 312. In this example, each of theflexure support ends may contact a respective electrical pad. Inimplementations of these embodiments, flexures 313 carry electricalcurrent with low resistance and are designed to be as soft as possibleto avoid additional force requirements on the motors (not shown) thatmove the stage.

FIG. 9 is a plan view of another example embodiment of a flexure 400 inaccordance with the disclosed technology. As illustrated, flexure 400comprises first support end 411, second support end 412, and a flexibleportion connecting support end 411 and support end 412. Flexure 400 hasan “S”-shaped design with the flexible portion comprising long andstraight portions 442, curved portions 441 connecting straight portions442 to support ends 411-412, and curved portions 443 connecting straightportions 442 with each other. In various embodiments, the curvatures ofcurved portions 441 and 443, the angles between straight portions 442,and the length of straight portions 442 are designed to fit geometricconstraints and minimize stiffness and stress of the deformed flexure.

FIG. 10 is a plan view of another example embodiment of a flexure 500 inaccordance with the disclosed technology. As illustrated, flexure 500comprises first support end 511, second support end 512, and a flexibleportion connecting support end 511 and support end 512. Flexure 500 hasa serpentine-shaped design with the flexible portion comprising long andstraight portions 542, curved portions 541 connecting straight portions542 with support ends 511-512, and curved portion 543 connectingstraight portions 542 with each other. In various embodiments, thecurvatures of curved portions 541 and 543, the number of turns in theserpentine design, and the length of straight portions 542 are designedto fit geometric constraints and minimize stiffness and stress of thedeformed flexure.

FIG. 11 is a plan view of another example embodiment of a flexure 600 inaccordance with the disclosed technology. As illustrated, flexure 600comprises first support end 611, second support end 612, and a flexibleportion connecting support end 611 and support end 612. Flexure 600 hasan “S”-shaped design with the flexible portion comprising long andstraight portions 642 aligned in a radial direction, curved portions 641connecting straight portion 642 and support ends 611-612, and curvedportions 643 connecting the straight portions with each other.

FIG. 12 is a plan view of another example embodiment of a flexure 700 inaccordance with the disclosed technology. As illustrated, flexure 700comprises first support end 711, second support end 712, and a flexibleportion connecting support end 711 and support end 712. In flexure 700,support ends 711 and 712 are not tangentially aligned. Flexure 700 hasan serpentine-shaped design with the flexible portion comprising longand straight vertical portions 742, and curved portions 743 connectingportions 742 with each other and with support ends 711-712.

FIG. 13 is a plan view of another example embodiment of a flexure 800 inaccordance with the disclosed technology. As illustrated, flexure 800comprises first support end 811, second support end 812, and a long andstraight flexible portion 842 connecting support end 811 and support end812. In flexure 800, support ends 811 and 812 are not tangentiallyaligned.

FIG. 14 is a plan view of another example embodiment of a flexure 900 inaccordance with the disclosed technology. As illustrated, flexure 900comprises first support end 911, second support end 912, and a flexibleportion connecting support end 911 and support end 912. In flexure 900,support ends 911 and 912 are not tangentially aligned. Flexure 900 has aserpentine-shaped design with the flexible portion comprisinghorizontal, long and straight portions 942, vertical, long and straightportions 944, curved portions 941 connecting vertical portions 944 withhorizontal portions 942, curved portion 943 connecting the verticalportions 944 with each other, and curved portions 945 connecting thehorizontal portions 942 with each other.

In various embodiments, the shape of the flexures may be generalized bycounting the numbers of horizontal and vertical straight portions of theflexure. For example, assume (n, m) represents a design with n verticalor close to vertical straight stripes, and m horizontal or close tohorizontal straight stripes. In such an implementation, flexure 400 maybe named as (0, 3), flexure 500 as (0, 5), flexure 600 as (3, 0),flexure 700 as (5, 0), flexure 800 as (1, 1), and flexure 900 as (2, 6).

FIG. 15 is a plan view of an example embodiment of a variable widthflexure 1000 in accordance with the disclosed technology. Asillustrated, flexure 1000 comprises first support end 1011, secondsupport end 1012, and a flexible portion 1013 connecting support end1011 and support end 1012. Flexure 1000 has a “V”-shaped design with theflexible portion 1013 comprising long and straight portions 1042 ofvariable width, curved portions 1041 connecting straight portions 1042and support ends 1011-1012, and curved portion 1043 connecting straightportions 1042 with each other. In flexure 1000, the straight portions1042 have a variable width, which in various embodiments may be adjustedto provide flexibility in the design of the flexure to tune theflexure's stiffness and other physical properties, such as, for example,the electrical resistance of the flexure. It should be noted that onehaving skill in the art would appreciate that a variable width could beimplemented in the design of other flexures (e.g., those illustrated inFIGS. 5-14) to tune the aforementioned physical properties (e.g.,electrical resistance and stiffness).

FIG. 16 is a Normalized Force versus Normalized Displacement plotshowing the performance of different flexure designs in accordance withvarious embodiments of the disclosed technology. As illustrated, theflexure may have a positive stiffness or negative stiffness in differentpost-buckle operation regimes.

FIGS. 17A-17C illustrate an example embodiment of a flexure 1100comprising offset layers in accordance with the disclosed technology.FIGS. 17A and 17B are top and bottom plan views of flexure 1100 afterfabrication. FIG. 17C is a three-dimensional perspective view of flexure1100 in a buckled state. As illustrated, flexure 1100 includes a metallayer 1110, a third layer 1130, and a polysilicon layer 1120 betweenmetal layer 1110 and third layer 1130. In embodiments, the third layermay comprise silicon oxide or a similar material. In flexure 1100, metallayer 1110 is offset from polysilicon layer 1120 and third layer 1130,thereby providing the benefit of reducing stress on flexure 1100 when itenters a buckled state shown in FIG. 17C.

Additionally, flexure 1100 comprises a variable width flexible portionthat is narrower near the root ends of the flexure (i.e., the curvedportions directly connected to support ends 1111 and 1112), and wider atthe center of the flexible portion. In this embodiment, the narrowerwidth near support ends 1111 and 1112 reduces the stiffness of flexure1100 in a buckled state. The greater width at the center of the flexibleportion improves the electrical resistance of flexure 1100.

FIGS. 18A-18C illustrate an example embodiment of a flexure 1200comprising split roots in accordance with the disclosed technology.FIGS. 18A and 18B are top and bottom plan views of flexure 1200. FIG.18C is a three-dimensional perspective view of flexure 1200 in a buckledstate. As illustrated, flexure 1200 comprises split roots of metal 1210and polysilicon 1220 at the curved portions 1250A-B directly connectedto support ends 1211 and 1212 (i.e., near root ends of flexure). Inembodiments, third layer 1230 and metal layer 1220 may also be split.

FIGS. 19A-19B illustrate an example embodiment of a flexure 1300comprising different length layers in accordance with the disclosedtechnology. FIG. 19A is a plan view and FIG. 19B is a three-dimensionalperspective view of flexure 1300. As illustrated, flexure 1300 includesa metal layer 1310 and a partial silicon oxide layer 1320 over metallayer 1310. In flexure 1300, only metal layer 1310 covers the entirelength of the flexure, thereby ensuring lower stress and lower stiffnessof flexure 1300. By contrast, silicon oxide layer 1320 only covers theends of the flexure (support sections 1311-1312 and end of flexiblesection), thereby ensuring that the flexure buckles in the correctdirection. In embodiments, layer 1320 can be silicon oxide or any othermaterial that can provide a residual stress to curve the metal flexure1300 up to the wanted direction. As would be appreciated by one havingskill in the art, the lengths of the layers of the flexure may be variedto tune the physical properties of the flexure such as, for example, itsstiffness and electrical resistance.

FIGS. 20A-20D illustrate actuators for moving an optoelectronic devicethat may use the flexures described herein in accordance with particularembodiments. FIG. 20A illustrates a plan view of actuator 30 inaccordance with example embodiments of the present disclosure. FIG. 20Billustrates a cross-sectional view of actuator 30 in accordance withexample embodiments of the present disclosure. As shown in FIG. 20A,actuator 30 includes outer frame 32 connected to inner frame 34 by oneor more flexures or spring elements 33. Further, actuator 30 includesone or more comb drive actuators 20 that apply a controlled force (e.g.,an electrostatic force developed from a voltage) between outer frame 32and inner frame 34.

Embodiments of actuator 30 are suitable for moving a platform (e.g., 45)having electrical connections, for actuator 30 enables precise,controlled, and variable forces to be applied between inner and outerframes 34 and 32 in multiple degrees of freedom (including linear androtational, for example), and may be implemented using a highly compactfootprint. Moreover, actuator 30 may utilize MEMS devices for reductionin power. Accordingly, actuator 30 provides multiple benefits overconventional solutions to optical image stabilization and autofocusapplications constrained by size, power, cost, and performanceparameters, such as in smartphone and other applications describedherein.

Flexures 33 may be electrically conductive and may be soft in allmovement degrees of freedom. In various embodiments, Flexures 33 routeelectrical signals from electrical contact pads on outer frame 32 toelectrical contact pads on the inner frame 34. In exampleimplementations, flexures 33 come out from inner frame 34 in onedirection, two directions, three directions, or in all four directions.

In one embodiment, actuator 30 is made using MEMS processes such as, forexample, photolithography and etching of silicon. In one embodiment,actuator 30 moves +/−150 micrometers in plane, and flexures 33 aredesigned to tolerate this range of motion without touching one another(e.g., so that separate electrical signals can be routed on the variousflexures 33). For example, flexures 33 may be S-shaped flexures rangingfrom about 1 to 5 micrometers in thickness, about 2 to 20 micrometerswide, and about 150 to 1000 micrometers by about 150 to 1000 micrometersin the plane.

In order for flexures 33 to conduct electricity well with lowresistance, flexures 33 may contain, for example, heavily dopedpolysilicon, silicon, metal (e.g., aluminum), a combination thereof, orother conductive materials, alloys, and the like. For example, flexures33 may be made out of polysilicon and coated with a roughly 2000Angstrom thick metal stack of Aluminum, Nickel, and Gold. In oneembodiment, some flexures 33 are designed differently from otherflexures 33 in order to control the motion between outer frame 32 andinner frame 34. For example, four to eight (or some other number) offlexures 33 may have a device thickness between about 50 and 250micrometers. Such a thickness may somewhat restrict out-of-planemovement of outer frame 32 with respect to inner frame 34.

In one embodiment, actuator 30 includes central anchor 36, and the oneor more comb drives 20 apply a controlled force between inner frame 34and central anchor 36. In embodiments, one or more comb drive actuators20 may be attached to central anchor 36, and central anchor 36 may bemechanically fixed with respect to outer frame 32. In one instance, thecomb drive actuators are connected to inner frame 34 through flexures 35that are relatively stiff in the respective comb-drive-actuatordirection of motion and relatively soft in the orthogonal direction.This may allow for controlled motion of inner frame 34 with respect toouter frame 32, and thus, more precise positioning.

Outer frame 32, in some implementations of actuator 30, is notcontinuous around the perimeter of actuator 30, but is broken into two,three, or more pieces. For example, FIGS. 22C and 22D illustrate planand cross-sectional views of actuator 30 in accordance with exampleembodiments of the present disclosure in which outer frame 32 is dividedinto two sections, and flexures 33 come out in only two directions.Similarly, inner frame 34 may be continuous or may be divided intosections, in various embodiments.

As shown in FIG. 20A, there may be four comb drives total—two combdrives actuate in one direction in the plane of actuator 30, and theother two comb drives actuate in an orthogonal direction in the plane ofactuator 30. Various other comb drive actuator 20 arrangements arepossible. Such arrangements may include more or less comb drives, andmay actuate in more or less degrees of freedom (e.g., in a triangular,pentagonal, hexagonal formation, or the like), as will be appreciated byone of skill in the art upon studying the present disclosure.

In one embodiment, platform 45 is attached to outer frame 32 and tocentral anchor 36. In this manner, platform 45 may fix outer frame 32with respect to central anchor 36 (and/or vice versa). Inner frame 34may then move with respect to both outer frame 32 and central anchor 36,and also with respect to platform 45. In one embodiment, platform 45 isa silicon platform. Platform 45, in various embodiments, is anoptoelectronic device, or an image sensor, such as acharge-coupled-device (CCD) or a complementary-metal-oxide-semiconductor(CMOS) image sensor.

FIG. 20B illustrates that the size of actuator 30 may be substantiallythe same as the size as platform 45, and platform 45 may attach to outerframe 32 and central anchor 36, thus mechanically fixing central anchor36 with respect to outer frame 32. In one example implementation,platform 45 is an image sensor with an optical format of 1/3.2″. In thisimplementation, the size of both actuator 30 and platform 45 can beequal to about 6.41 mm by 5.94 mm. As shown in FIG. 20D, in oneembodiment of actuator 30, platform 45 is smaller than actuator 30, andplatform 45 attaches to inner frame 34. In this particular embodiment,outer frame 32 is fixed relative to inner frame 34, and inner frame 34is moved by the various comb drive actuators 20.

FIG. 21 is an operational flow diagram illustrating an exemplary method1400 of assembling MEMS actuators for image sensor packages (e.g.,actuator 30) by latching electrical bars of an outer frame (e.g., frame32) of the actuator in accordance with an embodiment. In accordance withmethod 1400, the flexures (e.g., flexures 33) of the actuator arebuckled during latching, thereby seamlessly integrating the process ofbuckling the actuator's flexures into the MEMS actuator assemblyprocess. Although method 1400 is described with reference to assemblingan image sensor package, one having skill in the art would appreciatethat the method may be implemented for assembling any MEMS actuator withbuckled flexures. Method 1400 will be described with reference to FIGS.22-24, which illustrate exemplary electrical bar latching structuresthat may be used in latching the outer frame of the MEMS actuator.

With reference now to method 1400, at operation 1401 a MEMS actuatorwith unbuckled flexures is provided. FIGS. 22A and 22B illustrate onesuch example actuator 1500. Actuator 1500 comprises an inner frame 1510coupled to an outer frame 1520 by a plurality of unbuckled flexures (notpictured). Outer frame 1520 includes four electrical bars 1521-1524 thatare not latched. In embodiments, an array of unbuckled flexures maycouple each of electrical bars 1521-1524 with a corresponding side ofinner frame 1510. As illustrated in this particular embodiment,electrical bars 1521 and 1523 each comprise a latching mechanism 1525 ateach end of the bar with a respective latch hook or protrusion 1525A.Correspondingly, electrical bars 1522 and 1524 each comprise a latchingmechanism 1526 at each end of the bar with a respective latch notch orgroove 1526A.

Subsequently, at operation 1402 the plurality of electrical bars of theouter frame 1520 are latched together. FIGS. 22C and 22D illustrateactuator 1500 after electrical bars 1521-1524 are latched together. Asillustrated, each of the latch protrusions 1525A engage a respectivelatch groove 1526A, thereby securing the electrical bars 1521-1524together. During latching, the unbuckled flexures of the MEMS actuatorare compressed along an axial direction (e.g., X, Y, or X-Y direction)from the outer frame 1520 to inner frame 1510. During this compression,the plurality of unbuckled flexures enter a buckled state. Accordingly,the latched MEMS actuator includes a plurality of buckled flexurescoupling outer frame 1520 to inner frame 1510. In various embodiments,electrical bars 1521 and 1523 may be displaced between 0.2 and 0.4 mm inthe X direction, and electrical bars 1522 and 1524 may be displacedbetween 0.2 and 0.4 mm in the Y direction to latch the electrical bars1521-1524.

In embodiments, a customized pick-and-place (PnP) machine or tool may beused to latch the electrical bars 1521-1524. For example, the PnP toolmay securely clamp or hold the outer frame and produce a force along anaxial direction from the outer frame toward the inner frame sufficientto compress the flexures to a buckled state. Additionally, the PnP toolmay place the latch protrusions 1525A into corresponding latch grooves1526A.

As would be appreciated by one having skill in the art, any number ofalternative latching mechanisms besides 1525 and 1526 may be used tolatch the electrical bars of the outer frame of the MEMS actuator. Thesize and shape of latch protrusions 1525A and latch grooves 1526A may betuned in various embodiments to accommodate the design of variouselectrical bars for the MEMS drives actuator. For example, the shape ofthe latch protrusions and correspondingly latch grooves may berectangular, trapezoidal, triangular, or circular. As another example,the width, thickness, and height of the latch protrusions and groovesmay be adjusted.

FIGS. 23A-23D illustrates one such example of an alternative latchingmechanism implemented in a mems actuator 1600 comprising an inner frame1610 and outer frame 1620 with four electrical bars 1621-1624.Electrical bars 1621 and 1623 each comprise a latching mechanism 1625 ateach end of the bar with a respective latch protrusion 1625A.Correspondingly, electrical bars 1622 and 1624 each comprise a latchingmechanism 1626 at each end of the bar with a respective latch groove1626A. After latching, each of the latch protrusions 1625A engage arespective latch groove 1626A, thereby securing the electrical bars1621-1624 together. In this particular embodiment, the latch protrusions1625A are trapezoidal. Further, in this embodiment latching mechanism1626 is illustrated as comprising two components forming groove 1626A:the L-shaped hook structure 1626B and structure 1626C. Alternatively, inother embodiments latching mechanism 1626 may be one continuousstructure (i.e., hook structure 1626B may be combined with structure1626C).

As would be further appreciated by one having skill in the art, theouter frame of the mems actuator need not be limited to four electricalbars or parts, and may be composed of any number of latching electricalbars (e.g., 2, 3, etc.). For example, FIGS. 24A and 24B illustrate anembodiment of a mems actuator 1700 comprising an inner frame 1710 andouter frame 1720 with two electrical bars 1721-1722. As illustrated inthis particular embodiment, electrical bar 1721 comprises a latchingmechanism at each end of the bar including a triangular latchingprotrusion 1721A. Correspondingly, electrical bar 1722 comprises alatching mechanism at each end of the bar including a respectivetriangular latching groove 1722A. During latching, in this embodiment,the unbuckled flexures of the MEMS actuator are compressed along the Xdirection from the outer frame 1720 to inner frame 1710.

Referring back to method 1400, follow latching of the mems actuator, atoperation 1403 the latched MEMS actuator may be placed in a circuitboard cutout or opening and the assembly may be glued (e.g., usingthermal epoxy) to secure the MEMS actuator and latches to the assembly.FIG. 25 shows an exploded perspective view of an example embodiment ofplacement of a MEMS actuator 57 in a rigid circuit board 64 mounted on aback plate 66 in accordance with the technology disclosed herein. Acustomized pick and place machine (PnP) can place the MEMS actuator 57into the rigid circuit board opening 65 using alignment marks on therigid circuit board 74. It should be noted that the shape of opening 65is designed to fit MEMS actuator 57, and may provide in-plane movementlimiting features 67 on the corners if needed to improve the in-planedrop performance. The size of opening 65 is adjustable based on the sizeof the image sensor 70. In various embodiments, the gap between the MEMSactuator 57 and a back plate 66 can be controlled by a section ofembedded copper under the anchor 63 of MEMS actuator 57. In embodiments,epoxy between the rigid circuit board 74 and the back plate 66 can flowto the edges of the opening 65 during reflow and this bond linefunctions to control the gap.

Subsequently, further process operations 1404 may be performed toassemble the MEMS image sensor package. FIG. 26 is an explodedperspective view illustrating an assembled moving image sensor package55 that may use the actuator 57 of FIG. 25 in accordance with oneembodiment of the technology disclosed herein. Moving image sensorpackage 55 can include, but is not limited to the following components:a substrate 73; a plurality of capacitors or other passive electricalcomponents 68; a MEMS actuator driver 69; a MEMS actuator 57; an imagesensor 70; an image sensor cap 71; and an infrared (IR) cut filter 72.Substrate 73 can include a rigid circuit board 74 with an opening 65 andin-plane movement limiting features 67, and a flexible circuit boardacting as a back plate 66. The rigid circuit board 74 may be constructedout of ceramic or composite materials such as those used in themanufacture of plain circuit boards (PCB), or some other appropriatematerial(s). Moving image sensor package 15 may include one or moredrivers 69.

Since the thermal conduction of air is roughly inversely proportional tothe gap, and the image sensor 70 can dissipate a substantial amount ofpower between 100 mW and 1 W, the gaps between the image sensor 30, thestationary portions of the MEMS actuator 57, the moving portions of theMEMS actuator 57, and the back plate 66 are maintained at less thanapproximately 50 micrometers. In one embodiment, the back plate 66 canbe manufactured out of a material with good thermal conduction, such ascopper, to further improve the heat sinking of the image sensor 70. Inone embodiment, the back plate 66 has a thickness of approximately 50 to100 micrometers, and the rigid circuit board 74 has a thickness ofapproximately 150 to 200 micrometers.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for theinvention, which is done to aid in understanding the features andfunctionality that can be included in the invention. The invention isnot restricted to the illustrated example architectures orconfigurations, but the desired features can be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations can be implementedto implement the desired features of the present invention. Also, amultitude of different constituent module names other than thosedepicted herein can be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Although the invention is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more of the otherembodiments of the invention, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is:
 1. A method of creating a MEMS actuator assembly,comprising: providing a MEMS actuator with unbuckled flexures couplingan outer frame of the MEMS actuator to an inner frame of the MEMSactuator, wherein the outer frame comprises a plurality of unlatchedelectrical bars; and latching the plurality of electrical bars bysecuring a latch protrusion of a first of the plurality of electricalbars to a corresponding latch groove of a second of the plurality ofelectrical bars, wherein the flexures are in a buckled state when theelectrical bars are latched.
 2. The method of claim 1, wherein latchingthe plurality of electrical bars comprises compressing the unbuckledflexures of the MEMS actuator along an axial direction from the outerframe to the inner frame.
 3. The method of claim 2, wherein a pick andplace tool compresses the unbuckled flexures to the buckled state duringthe latching.
 4. The method of claim 1 further comprising thermal epoxygluing or reflow soldering the MEMS actuator to a circuit board afterthe latching.
 5. A MEMS actuator assembly, comprising: a MEMS actuatorwith unbuckled flexures coupling an outer frame of the MEMS actuator toan inner frame of the MEMS actuator, wherein the outer frame comprises aplurality of unlatched electrical bars; and wherein the plurality ofelectrical bars are latched by a latch protrusion of a first of theplurality of electrical bars secured to a corresponding latch groove ofa second of the plurality of electrical bars, wherein the flexures arein a buckled state when the electrical bars are latched.
 6. The MEMSactuator assembly of claim 5, wherein the unbuckled flexures of the MEMSactuator are compressed along an axial direction from the outer frame tothe inner frame to latch the plurality of electrical bars.
 7. The MEMSactuator assembly of claim 6, further comprising a pick and place toolthat compresses the unbuckled flexures to the buckled state.
 8. The MEMSactuator assembly of claim 5 further comprising at least one of athermal epoxy glue and reflow solder of the MEMS actuator to a circuitboard.